We propose to study in culture two biochemically and morphologically distinct populations of bone cells, CT cells and PT cells that respond in distinctly different manners to parathormone and calcitonin. The parameters measured (and the cell type in which parathormone produced a change) were: acid phosphatase, hyaluronate synthesis, mineral and matrix resorption from dead bone (CT cells); alkaline phosphatase, citrate decarboxylation, prolyl hydroxylase, collagen synthesis and hydroxylation (PT cells); cAMP (CT and PT cells). On the basis of the basal activities and hormone-induced changes, we provisionally identified the CT cells as osteoclasts and/or osteocytes and the PT cells as osteoblasts. We propose to further characterize these bone cells by determining their growth and development in culture, the sites where they existed in situ prior to removal from the calvaria and the degree of heterogeneity of the isolated populations. We also plan to study the biochemical changes induced by parathormone and other bone-active hormones in order to better realize the biochemical bases for these alterations. Finally, we will measure the binding and interaction of parathormone and other agents with the isolated bone cells and bone-cell membranes.